Process for impregnating fabrics with aqueous polymeric impregnating composition



Aug. 24, 1965 J. HOCHBERG 3,202,541

PROCESS FOR IMPREGNATING FABRICS WITH AQUEOUS POLYMERIC IMPREGNATING COMPOSITION Filed Aug. 51, 1960 INPREGNATING FABRIC WITH AQUEOUS DISPERSION 0F WATER-INSOLIIBLE POLYMERIC INPREGNANT AND WATER-SOLUBLE GELLING AGENT POLYNERIZING GELLING AGENT AND FIXING IIIPREGNANT IN FABRIC.

EVAPORATING WATER FROM INPREGIIATED FABRIC INVENTOR JEROME HOCHBERG BY TQW MMQ E" ELM ATTORNEY United States Patent O 3,2tl2,54'1 PRGCEES FDR EMPREGNATKNG FABRKCS WITH AQUEEGUS PGLYMERHI IMWKEG- NATENG CQMPUSE'HON Jerome Hochlserg, Newhurgli, N.Y., assignor to E. I. du Pont de Nernours and Company, Wilmington, Del a corporation of Delaware Filed Aug. 31, 1966, Ser. No. 53:,tlfi1 4 Claims. (Qt. Eli-14ft) This invention relates to a process, and more particularly to a process for impregnating fabrics with aqueous impregnating compositions.

impregnated woven, non-Woven and knitted fabrics have found wide use, for example, in applications as diverse as Writing, currency and insulation papers, gaskets, and padding for mattresses and upholstery. In recent years, leather replacements have provided another increasingly important and growing use for impregnated fabrics. A convenient method for impregnating fabrics is to disperse or dissolve an impregnant in water, distribute the resulting composition throughout a fabric, then dry the resulting product. Unfortunately, the aqueous impregnating composition begins to dry at the surfaces of the fabric and the impregnant tends to migrate toward these drying surfaces, thus yielding a product in which such surfaces are rich in impregnant, but in which the center may contain little or no impregnant. Also, prolonged drying times may permit drainage of impregnant and lead to further non-uniformity in impregnation. Particularly with non-woven fabrics where the impregnant is a hinder, the aforementioned migra tion of the impregnant leads to Weakness and delamination at the center of the product. Also, when a binderrich skin is worn through, a weakly bound fibrous interior may be exposed. Furthermore, the non-uniform impregnation caused by binder migration increases the tendency of impregnated products to crease, rather than bend uniformly. In addition, if such products are to be used as gaskets, the gaskets may tend to leak through the central plane from which most of the impregnant has migrated.

Heretofore, one general approach to solving the aforementioned problems has been to precipitate impregnant throughout fabrics before they are dried. This has been done conventionally by, for example, freezing impregnated products, changing the pH of a pH-sensitive, aqueous, impregnating dispersion, and by addition of electrolytes to impregnating compositions. Also, dielectric heating and thickeners have been used to reduce migra tion of impregnants. However, the aforementioned known methods have each fallen somewhat short of the desired objective, either because they are difiicult to control, because they are uneconomical or because they make it difficult to impregnate thick, dense fabrics.

The subject invention provides an improved process for impregnating fabrics which prevents migration of impregnant, which is easy and economical to perform, which is readily controlled and which can be used efiiciently even with thick, dense fabrics.

The process of the subject invention comprises impregating a fabric with a composition comprising an impregnant and an aqueous solution of ethylenically-unsaturated gelling agent, polymerizing the gelling agent to gel the aqueous solution and evaporating water from the resulting product. The drawing illustrates the process of this invention.

Any of the wide variety of materials that can be dissolved or dispersed in aqueous media can be used as impregnants in the process of the subject case. Water- 3,2h2fid l Patented Augr di, i965 insoluble polymeric impregnants are preferred. First, impregnating compositions can usually be formed at much higher concentrations from such impregnants than can comparable compositions having similar impregnating characteristics and viscosity formed with water-soluble impregnants. Also, since with such water-insoluble impregnants the concentration of impregnant usually is higher, the amount of gelling agent needed in the continuous phase usually is lower; hence any residual effects of gelling agent in the final product are minimized. Second, products formed with such water-insoluble impregnants, as compared to those formed with water-soluble impregnants, are generally water-insensitive without further treatment; hence, for example, they do not wrinkle, degrade, or deform when they are subjected to Water. Examples of such water-insoluble polymeric impregnants which are commonly used in aqueous impregnating dispersions are copolymers of butadiene with styrene, acrylonitrile or mixtures thereof, polychloroprene; homopolymers and copolymers of isoprene, polytetrafiuoroethylene; copolyrners of tetrafiuoroethylene and hexafluoropropylcne; polytrifluoromonochloroethylene; copolymers of vinyl fluoride and hexafluoroproplyene; homopolymers and copolymers of vinyl chloride and vinylidene chloride; homopolymers and copolyrners of acrylic esters, that is, the esters of acrylic and alphasubstituted acrylic acids, such as methyl acrylate, ethyl acrylate, propyl acryla te, isopropyl acrylate, isobutyl acrylate, amyl acrylate, octyl acrylate, Z-e'thyl hexyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, lauryl methacrylate, methyl ethacrylate, benzyl acrylate, dimethyl itaconate and mixtures thereof; copolymers of acrylonitrile with the aforementioned acrylic esters, styrene, vinyl chloride or mixtures thereof; polysulfides; polyamides; polyesters; polyesteramides; [polyvinyl butyral; polyvinyl acetate; polyvinyl propionate; and mixtures thereof. The amount of water-insoluble polymeric impregant employed depends generally upon the particular polymer employed, its particle size, and the desired consistency of the impregnating composition. It can vary, for example, from about 25 to based on the weight of composition; usually, however, it varies from about 30 to 60%.

Examples of other impregnants which can be used in the process of this invention are water-soluble polymeric impregnants such as amino-aldehyde resins, for example, the reaction products of phenols, urea, melamine or mixturcs thereof with, for example, formaldehyde, acetaldehyde or furfural; partially hydrolyzed polyvinyl acetate; polyvinyl alcohol; polyvinyl pyrrolidone; polyacrylic and olymethacrylic acids, and salts thereof; polyacrylamide; polyrnethacrylamide; starch; dextrins and sodium cellulose xanthate; and water-insoluble particulate materials such as glass beads, diatomaceous earth, powdered metals, glass microballoons, fiber-flocks and water-insoluble dyes, pigments and fillers. Water-soluble polymeric inipregnants are usually employed in concentration of about 10 to 20% based on the total weight of composition. Water-insoluble particulate materials are usually employed at concentrations similar to those used for the water-insoluble polymeric impregnants.

The water-soluble, ethylenicaily-unsaturated polymerizable gelling agents employed in the process of this invention immobilize the impregnant and prevent migration thereof. The amount of gelling agent employed varies with the solubility of the resulting gel, that is, the amount the gel swells in water. Usually, the amount of elling agent decreases as the amount the gel swells in water and the functionality of the gelling agent increase.

In general, the gelling agent is used in amounts just about suficient to gel the continuous phase and immobilize the polymeric impre nant; although greater amounts are permissible, they are not preferred. Generally, the amount of gelling agent required decreases with the amount of the continuous phase. Usually, less than about 30% and even as low as 0.1%, but preferably about from 1 to 15% gelling-agent, based on the weight of the aqueous or continuous phase, is employed.

In order to immobilize the impregnant, the gelling agent must polymerize to form a swollen gel. In order that the gel be formed before the water is evaporated from the impregnated fabric, the gelling agent should preferably polymerize below about 100 C. Furthermore, the gel should not break down, that is, the impregnant dispersion should not decrease appreciably in viscosity at temperatures at which water is to be evaporated therefrom, for example, at temperatures of 50 to 150 C. Generally, the ethylenically unsaturated gelling agents are those ethylenically unsaturated polymerizable materials bearing carboxyl, alkali metal or am-' monium carboxylate, hydroxyl, amine, amide, polyether, sulfonic acid, ammonium or alkali metal sulfonate, or quaternary ammonium groups. The preferred gelling agents are mixtures of water-soluble alpha-monoethylenically-unsaturated carboxylic acids, amides or organic or inorganic salts, preferably carboxylic acids, amides, alkali metal salts or ammonium salts, and about from 0.5 to 15, and preferably 1 to 5 mole percent based on the aforementioned mono-ethylenically-unsaturated, crosslinking agent bearing at least two ethylenic double bonds. Examples of water-soluble alpha-monoethylenically unsaturated carboxylic acids are acrylic acid, methacrylic acid, alpha-ethyl acrylic acid, crotonic acid and chloroacrylic acid. Examples of water-soluble amides and salts are acrylamide; methacrylamide; sodium, potassium and ammonium acrylate and methacrylate; N-methylol acrylamide and methacrylamide; hydroxyethyl acrylate; water-soluble salts of monoamines such as methyl amine, ethyl amine and propyl amine and acrylic and methacrylicacid; and mixtures thereof. Examples of water-soluble, ethylenically-unsaturated crosslinking agents bearing at least two ethylenic double bonds whichcan be used with the aforementioned alphamonoethylenically unsaturated monocarboxylic acids or derivatives thereof are, for example, glycol dimethacrylate, tetraethylene glycol dimethacrylate, N,N'-methylene bisacrylamide, N,N'-methylene bismethacrylamide, pentaerythritol dimethacrylate, pentaerythritol triacrylate, divinyl sulfone, triethylene glycol dimethacrylate, glycol diacrylate, ethylene glycol divinyl ether, glycerol divinyl ether, 1,3-diacrylyl-1,3,5-hexahydrotriazine, 1,3-dimethacrylyl-1,3,5 hexahydrotriazine and mixtures thereof. Acrylic and methacrylic acid, the sodium, potassium, ammonium salts thereof, acrylamide and methacrylamide together with acrylic and methacrylic acid diesters and bis- (acryl and methacryl)amides are particularly preferred classes of monofunctional materials and 'polyfunctional crosslinking agents, respectively, because they are readily water soluble and their polymerization is rapid and easy to control.

Other water-soluble gelling agents which can be used in the process of this invention are, for example, mixtures of monoand diacrylic and methacrylic acid esters of pentaerythritol and the corresponding partial acrylic and methacrylic acid ester mixtures of glycerine, sorbitol, mannitol and erythritol, and mixtures of vinyl sulfonic acids or the corresponding alkali metal or ammonium l sulfonates with the aforementioned polyethylenically peroxide; sodium, potassium and ammonium persulfates, chlorates, perborates and percarbonate; azo catalysts such as azobis(isobutyronitrile) and azobis(isobutyroirnidine hydrochloride); and amine catalysts such as betadimethylaminopropionitrile. Mixtures of catalysts, for example, mixtures of beta-dimethylaminopropionitrile and ammonium persulfate or, for example, redox (reduction-oxidation) systems such as ammonium persulfate, sodium thiosulfite or bisulfite and other well known persulfate-bisulfate combinations are particularly advantageous. Usually, about 0.05 to 5% of catalyst based on the weight of gelling agent is employed.

Conventional modifiers normally employed in aqueous impregnating dispersions can be included in the compositions used in the process of this invention; thus, for example, conventional dispersing agents such as, for ex ample, sodium lauryl sulfate, polyoxethylene, polyoxypropylene, colloidal silica, anionic organic phosphates,

magnesium montmorillonite, lauryl pyridine chloride, the

reaction'products of ethylene oxide with alkyl phenols such as the reaction product of 12 to 13 moles of ethylene oxide with 1 mole of octyl phenol, secondary sodium alkyl sulfates and mixtures thereof are usually used with water-insoluble polymeric or particulate impregnants.

Usually, about from 0.2 5 to about 6% of dispersing agent based on the total weight of the impregnant is employed. Examples of other well-known modifiers which can be added to the compositions used in this invention in conventional amounts are pigments and extenders, plasticizers, flow-control agents, coalescing agents and the like. Examples of pigments and extenders are metal oxides, hydroxides, chromates, silicates, sulfides, sulfates, carbonates, carbon blacks, organic dyes and lakes there-.

of and metal flake pigments; of course, as mentioned hereinbefore, similar materials can also be used as the sole impregnant. Examples of other additives are plasticizers such as di-benzyl phthalate,'butyl benzyl phthalate, tricres'yl phosphate, di(2 ethylhexyl)phthalate and di- (2 ethylhexyl)azelate and coalescing agents such as diacetone alcohol, cyclic ethylene carbonates, alkyl mono-' ethers of ethylene glycol or diethylene glycol and the like.

The aqueous compositions used in the process of this invention can be'prepared by adding the gelling agent together with catalyst therefor to a conventional aqueous impregnating composition containing in addition to the impreg-nant, for example, dispersing agent and, if desired,

1 and continuous filaments and yarns of polyamides, polyesters, polyester amides, viscose rayon, cellulose acetate rayon, wool, cotton, glass, polytetrafluoroethylene, polyformaldehyde, polyacrylonitrile, polystyrene, polyethylene and homopolymers and copolymers of vinyl chloride and other materials both natural and synthetic:

Next, the continuous or aqueous phase of the impregnating composition in the fabric is gelled by polymerizing the gelling agenttherein. The polymerization of the gelling agent can be controlled in several ways. First,

preferably, .at least'part of the catalyst for the gellation reaction is added immediately prior to impregnation. Also, polymerization of. the gelling agent can be controlled as if known in the art, by selection of the proper catalyst, by adjusting the amount thereof or by adding an inhibitor thereto to such as potassium. ferricyanide.

The temperature of the impregnating composition can' also be used as a control parameter. Other methods for controlling polymerization of the gelling agent include varying the pH of an impregnating composition containinga pH-sensitive catalyst such as a combination of betadimethylaminopropionitrile and ammonium persulfate or bubbling air through the aqueous dispersions to retard gellation. Preferably, the catalyst system, often in combination with inhibitors such as potassium ferricyanide, is adjusted so that the gelling agent polymerizes at slightly elevated temperature. Usually, polymerization temperatures of, for example, about from 40 to 100 C. are preferred. Regulating the polymerization of the gelling agent in this manner provides a simple and precise,

method for keeping the impregnant fluid during impregnation, yet providing a rapid gellation after impregnation but before there has been any appreciable evaporation, drainage or impregnant migration. Alternately, hoW ever, if the polymerization proceeds at room temperature, the catalyst for the gelling agent can be added continuously during impregnation and gellation allowed to occur by merely holding the impregnated fabric at room temperature for a few minutes. Also, gellation can be retarded by running the impregnation at a temperature sli htly below room temperature, for example, 0 to C., then Warming the impregnated fabric to room temperature to cause gellation. The fabrics impregnated with the gelled composition are next dried in the conventional manner, for example, in a forced air oven at tempera tures, for example, of about from 50 to 150 C. After they are impregnated and dried, the products of this invention are finally processed in the conventional manner used for impregnated fabrics. For example, if Waterinsoluble polymeric impregnants are used, the resulting products can be heated to fuse and coalesce the polymeric impregnant therein; heated and pressed between the platens of a press to fuse, consolidate and, if desired, emboss the products; calendered; buffed; coated or a combination thereof. Products impregnated with Watersoluble polymeric i ipregnants areusuallytreated to insolubilize the polymers, for example, by merely heating at elevated temperatures or by reacting them in situ with curing agents, isocyanates, urea or melamine formaldehyde resins, formaldehyde or the like.

products formed by the process of this invention are characterized by uniform impregnation and freedom from migration of impregnant. Particularly with waterinsoluble polymeric impregnants, the gelling agent forms a small, and preferably a very minor portion of the solids; thus, the gel has no appreciable adverse effect on properties such as, for example, water sensitivity, of the final product. in addition to the fact that the products of the subject invention have improved strength, crease resistance, and the like because of uniformity of impregnation obtained therewith, the process of the subject invention is particularly advantageous in that it can be easily and precisely controlled and because it is applicable With any of a wide variety of aqueous impregnating compositions and with fabrics including both thin, highly-porous fabrics and dense, thick fabrics.

The products of this invention can be used for anyof the wide variety of purposes for which impregnated fabrics are now used including, for example, currency, writing and Wrapping papers; electrical, heat, sound and chemical insulation; geslreting materials; leather replacements, for example, for shoes, upholstery, luggage and wearing apparel; rigid substrates, for example, for printed circuits; carpets, table coverings and roll coverings; blankets and sleeping bags and clothing. The products can be coated, for example, with coating compositions of polyurethanes, polyvinyl chloride or acrylic polymers by standard methods used in the art.

In the following examples which illustrate this invention, parts and percentages are by weight unless otherwiseindicated.

6 Example 1 An impregnating dispersion is prepared by blending together the following materials:

The dispersion of polytetrafluoroethylene contains 60% of finely divided polytetrafiuoroethylene, about 6% of a dispersing agent comprising the reaction product of 12 to 13 moles of ethylene oxide With 1 mole of octyl phenol and 34% of Water. The gelling agent contains about to 97% of acrylamide and about from 3 to 10% of N,-N-

methylene bis-a-crylamide. The resulting impregnating dispersion has a viscosity substantially equal to that of the initial polytetrafluoroethylene dispersion.

About 0.5 part of ammonium persulfate-is added to the above impregnating dispersion, then a needle-punched, non-Woven mat of 6.7-denier, 4-inch poiytetrafiuoroethylene fibers about Vs inch thick is immersed therein. The impregnated non-Woven mat is then inserted in an oven at about 90 C. whereupon the continuous aqueous phase of the impregnant gels rapidly Within about 5 minutes and before substantially any of the Water has evaporated therefrom. The impregnated and gelled mat thereafter is dried rapidly at about C.

The resulting product is uniformly impregnated throughout, that is, is free from impregnant migration. If the procedure'describe-d above is repeated except that the gelling agent mixture of acrylamide and N,N'-methylene bisacrylamide and the catalyst therefor are omitted, the impregnanttendsto drain from the impregnated mat 'dur ing drying-and-migrates toward the drying surfaces, leaving binder-poor areas near the center-of the product. In some cases, substantially all of the. polymeric impregnant may migrate from the center of the mat. The product above is useful Without further treatment for a gasketing material. Alternately, it can be heated, for-example, at about 375 C. under a pressure of 500 to 1000 p.s.i.. to fuse the binder and consolidate the product.

Example 2 An asueous impregnating dispersion is-prepared by blending together the following materials:

Potassiumferricyanide' 0.015

The terpolymer dispersion is a 33% dispersion of a terpolymer of 35% of acrylonitrile, 60% of butyl acrylate and 5% of methacrylic acid adjusted to a pH of 8 with ammonia.

About 0.5 part of ammonium persulfate is added to the above impregnating dispersion, then a non-Woven mat of 70- denier multi-filament glass yarn weighing about 6 ounces per square foot is dipped into the above dispersion. The mat is remove-d from the dispersion and inserted in an oven at about 90 C. The dispersion rapidly gelswithin about 5 minutes before substantially any Water has evaporated therefrom. Finally, the mat is dried atabout 120 C. The resulting product is uniformly impregnated and free from binder poor area caused by impregnant migration and drainage. The above product can-be pressed at elevated temperature to yield a sheet material useful as electrical insulation, for example, for slot liners in motors.

If an equivalent Weight of methacrylamide or N,N- methylene bismethacrylamide is substituted for athe acrylamide or N,N'-methylene bisacrylamide, respectively, used in this example substantially similar results are obtained.

' Example 3 I V The following materials are blended together to form an aqueous impregnating dispersion:

Parts Aqueous dispersion of polymer of Z-chlorobutadiene- 1,3 50% solids) 100 Ammonium acrylate N,N'-methylene bisacrylamide Ammonium persulfate Sodium thiosulfate 1 A non-woven, needle-punched web of 3 denier, /2-inch polyethylene terephthalate fibers weighing .about 6 ounces per square yard is immersed in the above dispersion. Next, the resulting impregnated mat is allowed to stand at room temperature for an hour during which time the impre-gnant gels. The product is then placed in an'oven and heated at 120 C. until it is dried. The resulting product showsno sign of impregnant migration. It is useful as a substrate for leather replacements.

If an equivalent weight of ammonium methacrylate is substituted for the ammonium acrylate employed above, substantially similar results are obtained.

Example4 The following materials are thoroughly blended to A non-woven mat of 3-denier, 2-inch polyhexamethylene adipamidefibers weighing about 6 ounces per square yard is impregnated with the above dispersion, thenwith drawn therefrom and placed in an oven at about '90" C. for about 5 minutes during which time the impregnant therein gels. The resulting product is then placed in an oven at 120 C. until it is dry. This product exhibits no binder migration.

Substantially similar results are obtained if an equivalent weight of potassium methacrylate is substituted for the sodium acrylate used above.

Example 5 The following materials are blended together to for an impregnating dispersion:

I Parts Aqueous terpolymer dispersion 100 Acrylic acid 5 Ethylene glycol dimethacrylate 0.5 Sodium bisulfite 1 The terpolymer dispersion is a 30% aqueous dispersion of a terpolymer of 35% of acrylonitrile .and 60% of butyl acrylate and- 5% of methacrylic acid containing about 0.3% of sodium lauryl sulfate dispersing agent.

A non-Woven batt of 0.1-denier, 1-inch polyethylene terephthalate fibers is prepared and needle, loomedtoi polyethylene terephthalate fibers is immersed therein. 7

The impregnated mat is then withdrawn from the impregnating bath, heated at about 80 C. for about 5 minutes 'to polymerize the gelling agent in the dispersion, then force'dried at about 125 Ci for about 45 minutes, Finally, the impregnated mat is preheated in anatmosph'ere at about 180 C. for about 1.5 minutes, then compressed in a press held at about 120 C. at a pressure of about 1000 pounds per square inch for about 15 seconds. The resulting product is useful for a leather replacement.

If an equal weight of methacrylic acid is substituted for acrylic acid employed above, substantially similar results are obtained.

Example 6 The following materials are thoroughly blended to form an impregnating dispersion:

. Parts Aqueous dispersion of polytetrafluoroethylene (similar to that described in Example 1) 222 Sodium acrylate 10 Ethylene glycol diacrylate 1 Anon-woven, needle-punched, heat-shrunk mat of 6.7- denier, 4-inch polytetrofluoroethylene fibers weighing about 20 ounces per square yard is preparedf Next, about 1 part of tertiarybutyl hydroperoxide is added to the above impregnating dispersion, then the aforementioned non-Woven mat of polytetrafluoroethylene fibers is immersed therein. The non-Woven mat is then withdrawn from the impregnating dispersion and heated at about C. for 5 minutes to, polymerize, the gelling agent and gel the continuous phase of the 'impregnant.

' Finally, the resulting product is dried at about 125 C.

to yield aproduct similar to that described in Example 1. Example 7 An aqueous dispersion is prepared from the following materials:

Parts Butyl rubber Zinc oxide 10 Zinc diethyl dithiocarbamate 1- Heat stabilizer 1 Water 300 To the resulting dispersion are next added about 15 parts of N-methylol acrylamide together with 1.5 parts of N,N'-methylene bismethacrylamide. A non-woven batt is prepared from a mixture of 0.5-denier and 1.5- denier, 1.5-inch crimped polyethylene terephthalate fibers. The non-woven batt is needle punched, then heat shrunk in boiling water to decrease the area of the batt about 5 3%. About 6 parts of tertiarybutyl hydroperoxide is next added to the aforementioned impregnating dispersion of butyl rubber, then the aforementioned non-woven 'needle punched, heat-shrunk mat is immersed therein. The impregnated mat is withdrawn from the impregnating bath, heated for 5 minutes at about 90 C. to gel the impregnant, then dried at 150 C. for about 25 minutes. The resulting product is useful as a substrate for leather replacements.

- Example 8 A solution is formed by dissolving 10 parts of polyvinyl alcohol of 5000 molecular weight in 90 parts of water. To this solution are added 10 parts of the gelling agent mixture described in Example 1, 0.4 part of betadimethylaminopropionitrile, 0.015 part of potassium ferricyanide and 0.01 part of oxalic acid. 0.5 part of ammonium persulfate is added to the above solution, then a needle punched non-woven mat of regenerated cellulose staple fibers about /s inch thick is immersed therein. The impregnated non-woven mat is then inserted in an oven at 90 C. whereupon the gelling agent gels rapidly before substantially any, of the water has evaporated therefrom.- 'The impregnated and gelled matis thereafter dried' rapidly at about C. Finally, formaldehyde vapor at 80C. is passed over the mat for 15 minutes to cross-link the polyvinyl alcohol therein and yield a non-woven batt bound with a water-insoluble poly vinyl formal impregnant binder.

Example 9 An aqueous dispersion is formed from the following materials:

Parts Titanium dioxide pigment 25 Sodium hexamethylphosphate 0.25 Water 75 Gelling agent (Same as Example 1) 5 Beta-dimethylaminopropionitrile 0.2 Potassium ferricyanide 0.007

Next, 0.25 part of ammonium persulfate is added to the above composition, then a coarse, porous, filter paper is dipped therein. The resulting impregnated paper is passed through a squeeze roll to remove excess impregnating composition, then inserted in an oven at 90 C. for about 5 minutes to gel the continuous aqueous phase of the impregnating composition. Finally, the resulting product is dried rapidly at about 110 C. and then calendered at that temperature at a pressure of about 2000 pounds per square inch to yield a product useful as a drawing paper for charcoal crayons.

I claim:

1. A process which comprises impregnating a fabric with a composition comprising a Water insoluble polymeric impregnant and an aqueous solution of Water-soluble, ethylenically-unsaturated gelling agent, polymerizing said gelling agent below about 100 C. to gel the aqueous solution and evaporating water from the resulting prodnot.

2. A process which comprises impregnating a fabric with an aqueous dispersion comprising a Water-insoluble polymeric impregnant in the dispersed phase and, as the continuous phase, an aqueous solution comprising less than about 30% by weight of water-soluble gelling agent, said gelling agent comprising a mixture of (a) at least one of the group consisting of water-soluble, alpha-monoethylenically-unsaturated carboxylic acids, amides and salts and (b) about from 0.5 to 15 mole percent, based on (a), of Water-soluble ethylenically-unsaturated crosslinking agent hearing at least two ethylenic double bonds, polymerizing said gelling agent below about 100 C. to gel said continuous phase and evaporating water from the resulting product.

3. A process which comprises impregnating a fabric with an aqueous dispersion comprising a water-insoluble polymeric impregnant in the dispersed phase and, as the continuous phase, an aqueous solution comprising about from 1 to 15% by Weight of water-soluble gelling agent, said gelling agent comprising (a) at least one of the group consisting of acrylic and methacrylic acids, the sodium, potassium and ammonium salts thereof, acrylamide and methacrylamide and (-b) about 1 to 5 mole percent, based on (a), of at least one Water-soluble crosslinking agent selected from the group consisting of acrylic acid diesters, methacrylic acid diesters, bis(acrylarnides) and bis(methacrylamides), polymerizing said gelling agent below about C. to gel said continuous phase and evaporating the Water from the resulting product.

4. A process which comprises impregnating a fabric With an aqueous dispersion comprising a water-insoluble polymeric impregnant in the dispersed phase and, as the continuous phase, an aqueous solution comprising about from 1 to 15% of water-soluble gelling agent, said gelling agent comprising (a) at least one of the group consisting of acrylic and methacrylic acids, the sodium, potassium and ammonium salts thereof, acrylamide and methacrylamide and (b) about 1 to 5 mole percent based on (a) of at least one of the group consisting of acrylic acid diesters, methaErylic acid diesters, bis(acrylamides) and bis(methacrylamides), polymerizing said gelling agent at a temperature of about from 40 to 100 C. to gel said continuous phase and evaporating water from the resulting product.

References Cited by the Examiner UNITED STATES PATENTS 2,763,574 9/56 Ruperti 117-143 2,774,687 12/56 Nottebohm et a1. 117-140 XR 2,801,984 8/57 Morgan et al 260-296 XR 2,808,383 10/57 Fikenstscher et al. 117-161 2,865,177 12/58 Gnaedinger 260-296 XR 2,876,131 3/59 Kumnick et al 117-161 2,914,498 11/59 Quarles et a1. 117-161 2,923,641 2/60 Graf 117-161 2,923,653 2/60 Matlin et a1 117-140 2,930,106 3/60 Wrotnowski et a1 117-140 2,931,749 4/60 Kine et a1 117-140 XR 2,937,156 5/60 Berry 117-161 2,973,285 2/61 Berke et a1. 117-140 XR 3,050,419 8/62 Ruperti 117-138.5

OTHER REFERENCES Cyanamer P250 Polyacrylanide, Market Development Dept, American Cyanarnid Co., New York, MOD- 92365M6/59, pg. 14.

RICHARD D. NEVIUS, Primary Examiner. JOSEPH REBOLD, Examiner. 

1. A PROCESS WHICH COMPRISES IMPREGNATING A FABRIC WITH A COMPOSITION COMPRISING A WATER INSOLUBLE POLYMERIC IMPREGNANAT AND AN AQUEOUS SOLUTION OF WATER-SOLUBLE, ETHYLENICALLY-UNSATURATED GELLING AGENT, POLYMERIZING SAID GELLING AGENT BELOW ABOUT 100*C. TO GEL THE AQUEOUS SOLUTION AND EVAPORATION WATER FROM THE RESULTING PRODUCT. 